1. Field of the Invention
The present invention relates to forwarding data in data communications networks using the Enhanced Interior Gateway Routing Protocol (EIGRP).
2. Description of the Related Art
Networks of general purpose computer systems and specialized devices connected by external communication links are well known and widely used in commerce. The networks often include one or more network devices that facilitate the passage of information between the computer systems and devices. A network node is a network device or computer or specialized device connected by the communication links. An end node is a node that is configured to originate or terminate communications over the network. An intermediate network node facilitates the passage of data between end nodes.
A portion of a network under the network administration of a single authority, such as an enterprise or Internet service provider (ISP) is called a domain or an autonomous system (AS). Routing facilitates the passage of data based on information shared among different domains. To reduce the consumption of network resources and improve scalability, some routing protocols send only summarized routing information. Routing information for an AS is summarized at its boundaries with one or more other ASs at intermediate network nodes called border gateway nodes or border gateway (BG) routers. Routing information shared within the borders of one AS is exchanged using an interior gateway protocol (IGP).
Example IGPs include the link state protocols such as the intermediate system to intermediate system (IS-IS) protocol and the open shortest path first (OSPF) protocol. Another IGP, developed by Cisco Systems of San Jose, Calif. for use in its intermediate network nodes, is the Enhanced Interior Gateway Routing Protocol (EIGRP). Some of the link-state protocols divide an autonomous system into multiple areas, flood all data for a unified routing database within and area, but send only summarized information between areas. Some IGPs, like EIGRP, send only summary information from each intermediate node in the autonomous system.
EIGRP provides several techniques for enhanced recovery from node and link failure in a communications network by predetermining some parameters, such as feasible successors, used for quickly determining new paths through the network. During recovery, however, some data packets formerly forwarded through a failed link or node are lost until the AS converges on new paths that utilize the remaining links and nodes.